Add EmitDifferenceOptions.DisallowExplicitMethodImplementations

[tmat]

Background and Motivation

The IDE needs to inform the compiler to not allow adding entries to MethodImpl table when emitting EnC delta on .NET Framework.

See #81304

Proposed API

namespace Microsoft.CodeAnalysis.Emit;

public readonly struct EmitDifferenceOptions
{
+   /// <summary>
+   /// True to disallow explicit method implementations in the delta.
+   /// Some runtimes (.NET Framework) do not support this feature.
+   /// </summary>
+   public bool DisallowExplicitMethodImplementations { get; init; }
}

[333fred]

API Review

• Should we remove the negative?
• MethodImplEntriesSupported ?

Conclusion: Approved with a positive name. Our suggestion is MethodImplEntriesSupported.

[tmat]

The negative is intentional. ExplicitMethodImplementations should be supported by default.

[333fred]

The Default instance can set whatever it wants as the defaults. We want to keep the properties in the options with the same directionality: the existing one is a positive, this one should be as well.

[tmat]

It's a minor change though since default(EmitDifferenceOptions) will change behavior.

[333fred]

I couldn't find anything actually using default. Did we miss something?

[tmat]

I don't think we are using default anywhere and I wouldn't expect anyone else is. Just saying that this is a minor breaking change if someone is using default and we don't know about it.

[333fred]

Sure. In all practicality, we don't think this is an issue, as we're the only known consumer of these APIs.